Strip tension control for a rolling mill



p 1968 E. E. BENSEMA ETAL 3,

STRIP TENSION CONTROL FOR A ROLLING MILL Filed' Jan. 28, 1966 I N VENT038.

EUGENE E. BEA/SEMI and mum l un M 3 G n 2, E2 ken mm 3 4 man A U on m mhm v 0 M W J \QSQQEQ ke bh mm ALLEN R. WEBER A f forney 3,399,556 STRIPTENSION CONTROL FOR A ROLLING MILL Eugene E. Bensema, Chicago, and AllenR. Weber, Thornton Township, Cook County, Ill., assignors to UnitedStates Steel Corporation, a corporation of Delaware Filed Jan. 28, 1966,Ser. No. 523,683

4 Claims. (Cl. 7221) ABSTRACT OF THE DISCLOSURE A strip tension controlfor a tandem rolling mill in which an electrical signal derived from theheight of a tension roll positioned vertically against the stripcontrols the strip tension by varying the speed of the roll standfollowing the tension roll. In order to maintain tension against thestrip during start up, the normal operating source of current for thefield of the generator powering the roll motor is replaced during startup by a second source of current through a capacitance-resistancenetwork whose characteristics result in initially moving the tensionroll very rapidly to overcome inertia in the mill. When the tension rollapproaches normal operating height the second power source is replacedby the normal operating source of current for the generator field.

This invention relates to a strip tension control for a rolling mill andmore particularly to a control for a tandem mill for cold rolling steelstrip. In such mills it is common practice to provide a horizontaltension or looper roll between the stands of the mill which is movablevertically by means of fluid operated cylinders in order to maintaintension on the strip being rolled. An electrical control signal derivedfrom a transducer whose output is proportional to the height of thetension roll regulates the speed of the roll stand following the tensionroll so as to maintain a predetermined height of the tension roll. Avalve regulates the pressure in the tension roll cylinder so as tomaintain a constant predetermined tension in the strip. In one commoncontrol an integrator is provided that initiates a rapid change in thespeed of the following stand in response to a rapid change of thetension roll so as to return the tension roll to its operating height.The integrator also provides a cumulative output for a very small inputso that a small deviation from the operating height will cause acorrection signal that increases with the time until it is large enoughto return the tension roll to operating position. ,When the strip isfirst threaded through the roll stands the top of the tension roll mustbe at an elevation at a below the horizontal plane between roll stands.When the automatic control is initiated a very large slow down signal isreceived and we have found that the tension roll does not move upwardlyfast enough to maintain the roll in contact with the strip. When thetension roll loses contact with the strip poor control results.

It is therefore an object of our invention to provide a control whichwill maintain the tension roll in contact with the strip during start-upas well as during normal operation of the mill.

This and other objects will be more apparent after referring to thefollowing specification and attached drawings, in which:

The single figure is a schematic view of the control of our invention.

Referring more particularly to the drawings, reference numerals 2 and 4relate to successive stands of a strip rolling mill. Stand 2 is drivenfrom motor 2M and stand 4 from motor 4M. Strip S passes from roll stand2 to inited States Patent Patented Sept. 3, 1968 roll stand 4. A looperroll 6 is provided between roll stands 2 and 4 and is adapted to contactthe lower side of the strip S. The roll 6 is moved vertically byhydraulic motor 8 having its piston rod 8R connected to the roll 6.Fluid under pressure is delivered to the motor 8 from a hydraulic pump10 through a solenoid valve 12 connected in conduit 14. Solenoid 128controls the position of valve 12. A rack 16 is connected to move withroll 6 and is in mesh with a gear 18 which is mechanically connected toselsyn transmitter 20. The output of selsyn transmitter 20 is connectedto a demodulator 22. This is a standard piece of equipment consisting ofa transformer 24, diodes, resistors and capacitors connected as shown.The function of the demodulator is to change the AC. signal oftransmitter 20 to a corresponding DC. signal. The output of thedemodulator 22 is connected to an integrating amplifier 26 which is alsoa standard piece of equipment, such as a Westinghouse A-l02 amplifiermodel 457A682GB1. The output of the integrating amplifier 26 isamplified and connected through a power amplifier 28 to generator field30F of generator 30. The output of generator 30 is connected to motor4M. Generator 30 has a second field 30F1 which is connected to DC. powersource Ll-L2 through an adjustable resistor 30R. Before starting upoperation, the operator manually adjusts resistor 30R to provide a basespeed for the roll stand 4. A similar speed control consisting ofgenerator 31, field 31F and variable resistor 31R is also provided forroll stand 2 and any other stands of the mill. After the speed of thestands is so adjusted, the strip S is fed through the mill stands. Theparts so far described are conventional.

According to our invention, the demodulator 22 is connected to abistable amplifier 32, the output of which is connected to a relay coil34 having a normally closed contact 340 and a normally open contact34C1. A positive feedback circuit 36 is provided from the output ofbistable amplifier 32. The amplifier 32 is a standard piece of equipmentand may be part No. 613C803,804 G01 shown in Westinghouse ElectricBulletin No. 1Ll6800- 3A. A relay coil 38 connected across DC. powerlines Ll-L2 has a normally open contact 38C located in the feedbackcircuit 36, a normally open contact 38C1 located in the circuit betweenamplifier 26 and generator 30F, and a normally closed contact 38C2. Arelay coil 40 is also connected across lines L1L2 in series withswitches 42 and 44. Relay coil 40 has a normally open contact 40Cconnected in parallel with switch 42, a normally open contact 40C1connected in series with solenoid 128, a normally closed contact 40C2,normally open contact 40C3, and normally open contact 40C4 connected inseries with contact 34C1 and relay coil 38. Contacts 34C, 40C3 and 3802are connected in series with one another to field 30F from a 48 volt DC.power source L3. Resistances 46 and 48 are also connected in series withthese contacts. A resistor 50 is connected between resistances 46 and 48to ground in series with a capacitor 52. Series connected resistor 54and contact 40C2 are connected in parallel with capacitor 52.

In normal operation, the equipment is set up to provide a predeterminedtension on the strip between stands 2 and 4 at a predetermined operatingheight of the roll 6. During normal operation, the roll 6 will be atthis height and the tension on the strip will be that desired. At thistime the output of the transmitter 20 will be such that there will be nooutput from demodulator 22. Assuming that the height of the roll departsfrom the optimum in a lower direction, the output of selsyn transmitter20 will be such that a DC. signal will be produced at the output of thedemodulator 22, the magnitude of which is dependent upon the amount ofdeparture from the operating height and of such polarity to cause thegenerator 30 to operate the motor 4M to decrease its speed. Decreasingthe speed of motor 4M will increase the amount of strip between rollstands 2 and 4 and thus permit the roll 6 to rise to its operatingposition. If, on the other hand, the roll 6 rises above its operatingposition, a signal of opposite polarity will be produced at the outputof demodulator 22, thus causing the speed of motor 4M to increase and todecrease the amount of strip between the stands 2 and 4. The operationso far described is that of the conventional control.

During sta-rt'up of the strip mill, roll 6 must be either at or belowthe horizontal plane between roll stands 2 and 4. In this position theelectrical output signal from demodulator 22 to amplifier 32 is largeenough to overcome the effect of the internal bias. The internal biastends to transfer the bistable amplifier 32 to the on state, thus thereis no output from amplifier 32. After the strip is threaded through rollstands 2 and 4, it is then necessaiy that the roll 6 be raised to itsoptimum operating position as fast as possible. This is accomplished bythe controls of our invention. As soon as the strip enters roll stand 4the operator closes switch 42. This energizes relay coil 40 and contact40C is closed to maintain the relay coil 40 energized when switch 42 isreleased. At the same time, contact 40C1 is closed, thus opening valve12 to permit fluid under pressure to flow from pump to hydraulic motor8. Also, contact 40C2 opens, contact 40C3 closes and contact 40C4closes. When contact 40C2 opens, discharge resistor 54 is removed fromacross capacitor 52. Closing of contact 40C3 completes the path forcurrent from DC. source L3 through capacitor 52, thus charging thecapacitor. The voltage applied to generator field 30F continues to rise,but at a slower rate, until it approaches a maximum when the capacitor52 is completely charged. Thus, we provide a current supply means havinga variable current which increases from a minimum to a maximum with therate of change being greatest initially so as to rapidly overcome theinertia of the mill. This control enables the roll 6 to maintain contactwith the strip S as the amount of strip between roll stands 2 and 4increases during initial rolling. Thus, the generator 30 will causemotor 4M to slow down, which permits roll 6 to rise. When roll 6approaches its operating position, the voltage at demodulator 22decreases towards zero. Slightly before the operating height of roll 6is reached, the electrical output signal from demodulator 22 becomessmall enough to allow the internal bias to transfer the bistableamplifier to the on state. The bistable amplifier 32 will then energizerelay coil 34, thus opening its contact 34C and closing contact 34C1.Opening of contact 34C removes the charging current from the capacitor52. Closing of contact 34C1 energizes coil 38, thus closing contacts 380and 38C1, and opening contact 38C2. Closing of contact 38C ensurescontinued energization of coil 34 regardless of the position of roll 6.Closing of contact 38C1 and opening of contact 38C2 transfers operationof the control to normal. When the end of the strip being rolledapproaches stand 2 the operator opens switch 44. This causesdeenergization of coil 40 so as to return its contacts to their originalpositions. Opening of contact 40C1 removes pressure from motor 8 throughvalve 12, thus permitting the roll 6 to lower to or below the horizontalpass line. If desired, switches 42 and 44 may be operated automaticallyby the strip S.

While one embodiment of our invention has been shown and described itwill be apparent that other adaptations rand modifications may be madewithout departing from the scope of the following claims.

We claim:

1. In apparatus for rolling strip comprising a first pair of reducingrolls through which the strip passes, a second pair of reducing rollsthrough which the strip passes from the first pair of rolls, a tensionroll between said first and second pairs of rollsover which the strippasses, means for moving said tension roll in a general verticaldirection, a motor for driving said second pair of reducing rolls, meansfor generating an electrical signal proportional to the position of saidtension roll with respect to a preset position, an integratingamplifier, means conmeeting said signal to said integrating amplifier, agenerator having a field connected to the output of said amplifier, andmeans connecting the output of said generator to said motor; theimprovement comprising means for supplying current to said generatorfield to raise said tension roll when strip is first fed through saidsecond pair of rolls, means for cutting off flow of current from saidamplifier to said generator field while said last named means isoperating, and means operable by said signal when said tension rollreaches said preset position to disconnect said current supplying meansfrom said field and to cause current to flow from said amplifier to saidgenerator field.

2. The apparatus of claim 1 in which said means for supplying current tosaid generator field to raise said tension roll when strip is first fedthrough said second pair of rolls supplies a variable current whichincreases from a minimum to a maximum with the initial rate of changebeing greatest.

3. The apparatus of claim 1 in which said means for supplying current tosaid generator field to raise said ten- 'sion roll when strip is firstfed through said second pair of rolls includes a power source, a pair ofresistors connected in series from said power source to said generatorfield, a capacitor, a resistor connected between said pair of resistorsin series with said capacitor to said power source, and a resistorconnected across said capacitor.

4. The apparatus of claim 3 including a first relay coil having anormally closed contact connected in series with said last namedresistor and two normally open contacts one connected in series withsaid pair of resistors on the power side thereof, means for energizingsaid first relay coil when strip is first fed through said second pairof rolls, a second relay coil connected in series with the second ofsaid two normally open contacts and having a normally open contactconnected between said amplifier and generator field and a normallyclosed contact connected in series with said pair of resistors on thegenerator field side thereof, a third relay coil having a normally opencontact in series with said second relay coil and a normally closedcontact in series with said pair of resistors on the power side thereof,and means operable by said signal when said tension roll approaches saidpreset position of energize said third relay coil.

References Cited UNITED STATES PATENTS 2,210,708 8/ 1940 Cook 72-2052,223,718 12/1940 Cook 72205 2,281,083 4/1942 Stoltz 72-205 2,363,68411/1944 Montgomery 72205 3,237,439 3/ 1966 Torrance 72205 CHARLES W.LANHAM, Primary Examiner. A. RUDERMAN, Assistant Examiner.

